1. Field of the invention
The present invention relates to a transmission and control mechanism for a hydrostatic-mechanical power transmission system, provided with a mechanical transmission unit driven through an input shaft connectable to a power source; a hydrostatic transmission unit that is connectable to the input shaft and includes a pump and a motor each having a displacement setting swash plate, at least either of the displacement setting swash plates being variable in angle; and a differential unit for connecting an output shaft to the mechanical transmission unit and the hydrostatic transmission unit to drive. The invention, more particularly, relates to a transmission and control mechanism for a hydrostatic-mechanical power transmission system suitably provided in a track-laying vehicle such as bulldozers.
2. Description of the Prior Art
One proposal of a transmission and control mechanism for a hydrostatic-mechanical power transmission system of the above type is disclosed in Japanese Patent Publication No. 31660/1987. The control operation of the transmission and control mechanism for a hydrostatic-mechanical power transmission system in the above patent publication will be hereinbelow described.
A target revolution speed for the engine working as a power source is firstly obtained from throttle position, and then the deviation of the actual revolution speed of the engine from the target engine revolution speed is obtained. On the basis of the above deviation, the angle of the displacement setting swash plate of the pump disposed in the hydrostatic transmission unit is controlled, thereby making the actual engine revolution speed approach to the target engine revolution speed.